1. Field of the Invention
The present invention relates to a method of preparing a nitrogen-doped graphene (hereinafter, referred to as “N-graphene”) and a N-graphene prepared thereby. More specifically, the present invention relates to a method of preparing a N-graphene comprising preparing an Edge-Functionalized Graphene (hereinafter, referred to as “EFG”) by binding an organic material having amino groups and functional groups such as carboxyl group with graphite through an electrophilic substitution reaction, specifically, the Friedel-Crafts acylation reaction and heating the resultant EFG, and a N-graphene prepared thereby.
2. Background of the Related Art
A graphene is classified as one of new materials which are the most remarkable in the future, as a material with very excellent physical and electronic properties
There are various reported methods of preparing a graphene with such excellent physical properties. Examples of the methods may include a mechanical exfoliation method, a chemical exfoliation method, a exfoliation-reinsertion-expansion method, a chemical vapor deposition method, an epitaxy synthesis method and the like.
The mechanical exfoliation method has a problem that the final yield is extremely low, and the chemical exfoliation method has a problem that there remains many defects in graphene so that graphene-inherent excellent physical and electric properties are decreased. The exfoliation-reinsertion-expansion method has a problem that substantial yield of graphene is very low and interlayer contact resistance is high due to used surfactants so that the method does not exhibit satisfactory electric properties. The chemical vapor deposition method has problems such as a complicated process, the requirement of a heavy metal catalyst, and many limitations in mass production. The epitaxy synthesis method has disadvantages such as a poor electric property of the produced graphene and very expensiveness of the substrate.
Meanwhile, although the platinum catalyst is considered as the most efficiency one for a H2/O2 fuel cell, it has disadvantages such as high cost, decreased performance caused by CO poisoning, and limited amount.
Although the research for high performance catalyst capable of replacing the Pt catalyst and Ru catalyst has been conducted for more than 10 years until now, it is difficult to realize the catalyst.
Therefore, the catalyst research for a H2/O2 fuel cell has fundamentally focused on the efficiency use of platinum. Largely, the research for increasing the reaction surface by controlling the size of particle of platinum to nano size and the research for enhancing reactivity using carriers of various structures and alloy have been conducted.
As the particle size of platinum is smaller, the particle surface thereof per weight increases and the distribution is also higher, which is advantageous in the manufacture of lowly carried platinum catalyst. Therefore, the research for reducing the used amount of catalyst by controlling the particle size of catalyst or using carrier has been conducted, and many results have been reported.
Because of such reasons, many researchers have studied a carrier having various structures such as carbon particle, carbon nano tube, porous carbon particle and the like for various objects. As a result of such study, the used platinum amount has been reduced to a hundredth during several decades. Now, although it is reported that the carried amount of Pt in the a range of 0.2˜0.4 mg/cm2 has a best efficiency, it is generally accepted that the amount of platinum should be reduced to a fifth or less from the current technology for commercialization. Ultimately, the amount should be reduced to a tenth or less from the current technology.
Although largely the reduction of the carried amount of platinum and the efficient dispersion of platinum, and the development of non-platinum catalyst are pursued all over the world, including the U.S.A., Japan and Europe, both reduction of cost and enhancement of performance do not yet meet practical use.
The research team of professor Dai in the U.S.A. has developed an electrode which has a longer life and about four times more excellent performance than platinum (Pt) catalyst using a vertically cultured carbon nano tube doped with nitrogen by metal-free oxygen reduction catalyst for a H2/O2 fuel cell (2009, Science).
Further, there was already a report that by estimating the performance of N-graphene as a H2/O2 fuel cell catalyst, N-graphene shows a similar catalyst activity to nitrogen-doped carbon nano tube (2010, ACS Nano).
These methods may be a very good research result showing that a nitrogen-doped carbon material can replace a platinum catalyst.
However, since the used method for preparing the carbon nano material is a chemical vapor deposition (CVD) method, it has a many difficulties to be practically applied industrially.